§ 4 ' ^^ ARTS AND SCIENCES. 369 



_L4-JL-j_JL-uJL-4-etc 



which is easily seen to be one-fourth of the original series. 

 Since, then, three-fourths of the series is equal to —--^ the 



> 



whole series is equal to —- . 



6 



We see, therefore, that the theory which we are investi- 

 gating is not open to the criticism which caused us to 

 abandon the theory of gravitation, since the potential, 

 which determines the latent heat, is practically indepen- 

 dent of the whole mass of a substance, provided only that 

 it contain several lavers of molecules or atoms, as we 

 alwa3^s suppose it to do. 



The latent heat is the same as if about 2 tt^ atoms could 

 surround a given atom, and for convenience in rough cal- 

 culation we may call this number twenty. 



It follows that a substance having two atoms in the 

 molecule will require about one-twentieth less heat to 

 volatilize it than if it had only one, since in the latter case 

 each atom is practicall}^ separated from twenty others 

 (whose interference may be neglected), while, in the for- 

 mer, one of these remains by its side. In the same wa}-, if 

 the molecule contain three or four atoms, clustered, the 

 substance will require two- or three-twentieths less heat 

 respectively; but when there are more than two atoms in 

 the molecule, we may have a variety of atomic groupings 

 possible, and to obtain even a rough measure of the latent 

 heat, a knowledge of the graphical symbol will be neces- 

 sary. 



If the atoms be of different kinds, the solution becomes 

 still more complex, and indeed impossible in the present 

 state of our knowledc^e of the molecular constitution.* 



'^* See, however, Ruhlmann, Mechanischen Warmetheorie, Volume II., page 226 et seq. 



